Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $96.57   11.117%   $107.3057   $107.31   $107.30   $107.30  
  Purchase #2 $84.99   12.442%   $95.5645   $95.56   $95.55   $95.60  
  Purchase #3 $92.82   6.349%   $98.7131   $98.71   $98.70   $98.70  
  Purchase #4 $207.48   6.808%   $221.6052   $221.61   $221.60   $221.60  
  Purchase #5 $230.42   13.526%   $261.5866   $261.59   $261.60   $261.60  
  Purchase #6 $46.52   13.653%   $52.8714   $52.87   $52.85   $52.90  
  Purchase #7 $109.65   6.691%   $116.9867   $116.99   $117.00   $117.00  
  7 purchase totals = $868.45       $954.6332   $954.64   $954.60   $954.70